As known, dual mode cavity filters, hereinafter named filters for sake of simplicity, are usually installed aboard communication satellites so as to realise output multiplexers (OMUX) and/or input multiplexers (IMUX).
Such filters comprise, for instance, two waveguide cavities and three coupling irises and are used for filtering in and/or out communications, for instance radio and/or television communications from earth apparatuses to the satellite and vice-versa.
According to known prior art, the dual mode filters are tuned before the satellite is sent to outer space, according to a set of specifications including centre frequency and bandwidth, and the tuning is made by inserting and locking, in predefined locations along the cavities, metallic screws at certain insertion lengths inside cavities.
In case a need appears to modify input/output filter characteristics, for instance centre frequency and/or bandwidth, a problem exists because filtering characteristics are strictly connected to the tuning made before sending the satellite in the outer space, i.e. to the screw location and insertion length.
Therefore, prior art seems to be not able to solve the problem of changing the characteristics of dual mode filters after sending communication satellites in the outer space.
In summary, Applicant has noted that prior art is not able to solve the problem of changing the filter characteristics, as for instance centre frequency and bandwidth of dual mode cavity filters, after sending the filters installed aboard a satellite in the outer space.